Apple’s refurbs come with a new outer shell and new battery, meaning you get same-as-new appearance and performance. Better still, you get the same one-year warranty Apple extends to new hardware. There is literally no downside.
I was asked recently by a friend what my take on refurbished Apple products. As Broida says, there is no downside. You get the same one year warranty as new products. Apple Care can still be purchased as well.
So if you are planning to buy a current Apple product with the stock configuration, there is no reason not to pick up a refurbished one for a few dollars cheaper.